NERSC Initiative for Scientific Exploration (NISE) 2011 Awards

New potential energy surface for ozone molecule

Dmitri Babikov, Marquette University

Associated NERSC Project: Coherent Control of the Ground Electronic State Molecular Dynamics (m409)

New accurate potential energy surface of ozone will allow computational studied of spectroscopy and dynamics of this molecule, important for environment. In the upper atmosphere, stratosphere of our planet, ozone plays crucial role in protecting life on Earth from dangerous ultra-violet radiation from the sun. In the lower atmosphere, troposphere, ozone is the main component of the photochemical pollution in industrial areas (smog). We should try to reduce levels of tropospheric ozone, preserving the stratospheric ozone.

A very accurate ab initio tools must be employed, such as MRCI level calculations with CASSCF for the electronic structure of this molecule, with at least six electrons of each oxygen explicitly correlated. Very large basis sets are needed, up to sixtaple-zeta, and extrapolation of each point to the CBS limit should be performed. Without this, the dissociation energy of ozone can’t be reproduced accurately. The van der Waals region of ozone has shallow wells, and those are expected to play major role in the ozone formation dynamics. These wells must be accurately captured by the calculations. Furthermore, the spin-orbit interaction in the asymptotic region must be taken into account. The value of spin-orbit interaction is comparable in magnitude to depth of vdW wells. Both kinds of interaction need to be treated accurately at the same time.

The ab initio points is one component of the surface development, but choosing right strategy for fitting or splining the data is another important issue. The standard procedure of splining is too demanding and is out of question. We have in our tool box a fitting method based on symmetry invariant polynomials. This method offers very significant advantages for molecules with identical atoms, like ozone. The ozone is a perfect system to treat with this relatively new approach.